The present invention relates to a radiation shielding device for radio transmitting devices. More particularly, the present invention pertains to a radiation shielding apparatus which is a tri-band antenna adapted to be tuned to give dual band polarizations.
It is well known to shield circuitry from an electromagnetic wave radiation by providing a layer of electromagnetic wave shielding material between an electromagnetic wave source and circuitry and other circuitry to be protected. The shielding is provided to prevent the influence of the electromagnetic wave noise from affecting the protected circuit.
The transmission of electromagnetic waves from a portable cellular telephone is traditionally accomplished on the antenna. Hand-held cellular phones typically have transmitting/receiving units and an antenna is provided in the interior and/or on an exterior surface of the handset. Typically, hand-held cellular phones have a transmitting/receiving unit which is located on the handset, and includes a mouthpiece, an earpiece and the antenna, within a single compact unit. The antenna usually extends from the top surface of the handset, and it transmits and receives the electromagnetic wave radiation. The antenna may be either telescoping or fixed externally on the phone body. Alternatively, the antenna may be internally located. The antenna transmits electromagnetic wave radiation so as to send communication signals from the cellular phone to a distant cell located on a cellular network, and receives electromagnetic wave radiation during receipt of communication signals from the cell. The electromagnetic wave radiation transmitted by the antenna is generated by a transmitter disposed within the interior of the cellular phone""s handset.
In U.S. Pat. No. 5,335,336 issued to Daniels, a shielding device was provided for a radio transmitting device, particularly a hand-held cellular phone, wherein the shielding device was externally mounted so as to fully or partially encompass the antenna. In another embodiment, the shielding device was incorporated directly into the shaft structure comprising the antenna. In each of the Daniels"" devices, the shield was comprised of either an absorption, blocking, or reflecting material formed into a semi-circular arc, a fully enclosed arc, or was applied directly to the metallic substrate forming the antenna. The construction of the radiation shield member could also have various cross sectional configurations. For example, it could have the form of an open or closed box-shape, and open or closed curve, or could have been a flat planer member. One downside of the Daniels"" electromagnetic shield was that due to its solid structure, it was only effective as a single band antenna, capable of only vertical polarization even if it is shaped into semi-circular, circular, or other geometric shapes. This means that should a user assume a position where the antenna is no longer vertical, the transmission and reception of the phone will be interrupted until the antenna is again positioned vertically.
Another problem with cellular phones which were produced less than 10 years ago, like the Daniels phone, is that they operated on a single 800 MHz band. Since then, cellular phone usage has exploded, with capacity on the 800 MHz band becoming saturated and hardly utilized by phone manufacturers. As a result of the explosive popularity in cell phone usage, more frequency bands were needed and in response, the FCC dedicated a new cellular band; the 1900 MHz band. However, that band is not adjacent to the 800 MHz band, meaning that phones must be capable of operating at dual bands of 800 and 1900 MHzs. The shielding device of Davis is limited to transmitting and receiving signals only on the 800 MHz band. Thus, if the antenna device of Daniels was incorporated into one of the cellular phones being produced today, the 1900 MHz signals would never be recognized and the phones would not work other than at 800 MHz. Furthermore, the phones operating in Europe are dedicated to still another cellular frequency band that is discrete from the 800 and 1900 MHz bands of the United States cellular system. The cellular bands dedicated to European usage operate at the 900 and 1800 MHz bands. Therefore, many worldwide businessmen encounter phone inactivation problems when traveling back and forth between continental Europe and the United States. Currently, one of the only solutions available is for businessmen to carry two phones; one capable of operating on the United States cellular bands and the other capable of operating on European cellular bands.
Therefore, there is a need to provide an improved shielding apparatus, which can also improve the capabilities of the antenna, in order to overcome the difficulties with the prior art, as mentioned above, and to provide an antenna which can be tuned to three cellular bands so that U.S. phones and European phones can be used interchangeably.